Problem: $ C = \left[\begin{array}{rrr}1 & 0 & 1 \\ 1 & 2 & 0 \\ 2 & 1 & 2\end{array}\right]$ What is $ C^{-1}$ ?
Answer: $ = \left[\begin{array}{rrr}4 & 1 & -2 \\ -2 & 0 & 1 \\ -3 & -1 & 2\end{array}\right]$